Mixed Content warnings

[djcowan]

Simply raising the issue for tracking here. Love the plugin – hoping ACF implements this as an alternative map field

Issue:
Mixed Content: The page at '' was loaded over HTTPS, but requested an insecure image ''. This content should also be served over HTTPS.
"page" was loaded over HTTPS, but requested an insecure image 'http://b.tiles.wmflabs.org/bw-mapnik/9/464/"image".png'. This content should also be served over HTTPS.

Related articles:
https://help.openstreetmap.org/questions/63360/httpbtileosmorg-for-https
Leaflet/Leaflet#3186

[mcguffin]

https://b.tiles.wmflabs.org/bw-mapnik/9/464/123.png results in a certificate error.
However https://tiles.wmflabs.org/bw-mapnik/9/464/123.png works. Applied a quick'n'dirty patch, substituting the original URLs from leaflet providers.
Related: leaflet-extras/leaflet-providers#311